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828

Appendix IL

I



furnace tubes, underneath the boiler, and returning along the
side flues to the chimney. Where the brickwork touches the
boiler it should be as narrow as possible to avoid corrosion or
any unseen wasting, and should there be luted with fireclay
instead of mortar. The whole setting is lined with firebrick and
inclines slightly towards the front in order to drain.

P. 337. The Field Boiler.—This is principally interesting
on account of the Field tube, which has been much applied
where quick steaming has been required. The tube consists of
an outer or blind member, A, Fig. 798, having water inside and

furnace gas outside, and the inner tube B is supported by feathers
at the top, its funnel mouth entrapping the downward current,
thus causing the upward current to ascend by tube A, and pro-
moting the disengagement of steam. The boiler c shews the
tubes in position, hung from the firebox crown, D being a baffle
plate to retard and reflect the draught.

P. 339. Water-tube Boilers having been greatly favoured
for certain purposes during recent years, a more extended account
seems advisable. These boilers were tried in France as early as
1871, and have been used in the French Navy since 1874. In
the meantime the Babcock-Wilcox boiler was introduced in
various parts of the worldr The necessity for a boiler for the
English Navy suited to high pressures, combining light weight